Abstract

Sarcopenia and cachexia present characteristic features of a decrease in skeletal muscle mass and strength, anorexia, and lack of motivation. Treatments for these diseases have not yet been established, although selective androgen receptor modulators (SARMs) are considered as therapeutic targets. We previously reported that a novel SARM compound, SARM-2f, exhibits anabolic effect on muscles, with less stimulatory effect on prostate weight compared with testosterone, in rat Hershberger assays and cancer cachexia models. In this study, we studied the mechanism of action for SARM-2f selectivity and also assessed whether the muscle increase by this compound might lead to improvement of muscle function and physical activity. First, we examined the tissue distribution of SARM-2f. Tissue concentration was 1.2-, 1.6-, and 1.9-fold as high as the plasma concentration in the levator ani muscle, brain, and prostate, respectively. This result showed that the tissue-selective pharmacological effect did not depend on SARM-2f concentration in the tissues. The ability of SARM-2f to influence androgen receptor (AR)-mediated transcriptional activation was examined by reporter assays using human normal prostate epithelial cells (PrEC) and skeletal muscle cells (SKMC). SARM-2f exerted higher activity against AR in SKMC than in PrEC. Mammalian two hybrid assays showed different co-factor recruitment patterns between SARM-2f and dihydrotestosterone. Next, we studied the effect of SARM-2f on motivation and physical functions such as sexual behavior and motor activities in castrated rat or mouse models. SARM-2f restored the sexual behavior that was lost by castration in male rats. SARM-2f also increased voluntary running distance and locomotor activities. These results suggest that tissue-specific AR regulation by SARM-2f, but not tissue distribution, might account for its tissue specific androgenic effect, and that the muscle mass increase by SARM-2f leads to improvement of physical function. Together, these findings suggest that SARM-2f might represent an effective treatment for sarcopenia and cachexia.

Effect of SARM-2f (A) and TP (B) on the levator ani muscle weight and prostate weight. The y axis represents percent (%) of the sham group. The drug was administered to castrated male rats for three weeks. Data are shown as the means ±SD (n = 4–5).

The ability of compounds to influence AR-mediated transcriptional activation was examined in skeletal muscle cells (SkMC) (A) and prostate epithelial cells (PrEC) (B) by reporter assays as described in Material and methods. Data are shown as the means ± SD (n = 3).

Induction of sexual behavior by SARM-2f and TP in castrated male rats.

(A) Sexual behavior scores. (B) Lean body mass change and levator ani muscle weight (g), lean body mass. The drug was administered to castrated male rats for three weeks. Sexual behavior was determined by observation of the estrous cycle of female rats that had been mated with male rats treated with SARM-2f or TP at the end of the treatment period. (n = 10).*P < 0.05 vs. the control group with a Fishers' exact-test. **P < 0.005 vs. control group with the Williams test. Ctrl, Control vehicle group, TP, testosterone propionate.

The outline of the voluntary running test is shown in Fig 6A. Running distance during 2 weeks of treatment with TP or SARM-2f was calculated by the formula described in the Materials and methods section (B). (B) Running count average in day13–14. (C) Levator ani muscle weight measured after 2-week dosing. The drug was administered to castrated mice with DHEA for 2 weeks. The measurement technique is described in the Materials and methods section. Data are shown as the means ± SD (n = 8). *P < 0.025 vs. the ORX (vehicle treated castrated mice) group using the Williams test. #P < 0.05 vs the ORX by student t-test.

Distance travelled during 2 weeks of treatment with TP or SARM-2f was calculated by the formula described in the Materials and methods section (A). (B) Activity during the light or dark phase in day 13–14. (C) Levator ani muscle and body weight measured after 2-week dosing. Food intake was calculated during 2-week dosing. The drug was administered to castrated mice with DHEA for 2 weeks. The measurement technique has been described in the Methods section. Data are shown as the means ± SD (n = 8). ##P < 0.005 vs. ORX (vehicle treated castrated mice) group using a Williams test. *P < 0.05, **P < 0.01 vs. ORX group using a student t-test.